Explaining gender differences in chronicity/disability after sick-leave with musculoskeletal diagnoses. Prospective study of 64,249 employees

Background: Musculoskeletal disorders (MSD) contribute heavily to rising costs in all welfare states and are a great burden for individuals and families. Studies have consistently found a higher prevalence of MSD among women compared to men. The causes are however unclear.

Methods: Population-based, prospective cohort study: All cases with a spell of long-term sickness absence (LTSA) > eight weeks with a musculoskeletal diagnosis, reported to the Norwegian Social Insurance Services in 1997, were included in a five-year follow-up. Endpoint was granting of a permanent disability pension (DP). Diagnoses and socio-demographic information were used as explanatory variables in Cox's proportional hazards analysis, separately for gender.

Results: 37,942 women and 26,307 men were included in the study. Cumulative incidence of LTSA with MSD was thus 4.1/100/year among vocational active women and 2.6/100/year among the men. Among the women 22% was granted a DP, and 18% among the men. Low socioeconomic status (education and income) strongly increased the risk of DP, but less for women than men. Having children decreased the DP-risk for both genders (no double burden effect). After adjustment for socio-demographic variables a seven percent higher female risk of DP remained (P<0,001), and this was entirely removed when the diagnostic distribution was introduced in the regression. However, models with interactions between gender, socioeconomic and diagnostic covariates showed a strong effect of female gender.

Conclusion: The results suggest that both socioeconomic and diagnostic (biological) factors contribute to the female excess in musculoskeletal morbidity and disability.